Machine for machining work pieces with cutting teeth, especially saw blades

ABSTRACT

A tool head ( 46 ) in which a tool spindle ( 52 ), adapted to be equipped with a disc-shaped tool ( 100 ), is supported so as to be driven in rotation about a spindle axis (C), is associated with a workpiece support ( 82 ) on which a workpiece ( 10 ) can be arranged such that the tooth tip ( 18 ) of a cutting tooth ( 12 ) to be machined will lie on a stationary reference axis (A). The tool head ( 46 ) is movably supported by means of a reciprocating slide ( 34 ) which is movable back and forth along a reciprocating slide guide means ( 32 ) transversely of the reference axis (A), by means of a feed slide ( 24 ) adapted to be advanced along a feed slide guide means ( 22 ) transversely of the reciprocating slide guide means ( 32 ), and by a pivot bearing means ( 42 ) defining a pivot axis (B) parallel to the reciprocating slide guide means ( 32 ). The tool head ( 46 ) is pivotable about the pivot axis (B) by a pivot drive means ( 60 ) from a normal position for machining surfaces of the cutting teeth ( 12 ) which extend parallel to the reference axis (A) into inclined positions for machining oblique surfaces of the cutting teeth ( 12 ). The distance (x) by which the active face ( 106 ) of the tool ( 100 ) is spaced from the pivot axis (B) can be measured by a measuring means ( 108 ). A numerical control means ( 98 ) makes sure that the feed slide ( 24 ) adopts a position at which the spacing of the pivot axis (B) from the reference axis (A) equals the distance (x) when the tool head ( 46 ) is in the normal position, and that the feed slide ( 24 ) adopts a respective corrected position when the tool head ( 46 ) is in an inclined position.

FIELD OF THE PRESENT INVENTION

The invention relates to a machine as defined in the preamble of claim1.

BACKGROUND OF THE INVENTION

In a known machine of this kind (DE 27 51 408 A1) the reference axis isdefined by a rocker bearing which is disposed on the machine bed andsupports a radially projecting beam. The beam is formed with areciprocating slide guide means along which a reciprocating slide isdisplaceable radially with respect to the reference axis. A pivotbearing means on the reciprocating slide defines a pivot axis whichextends parallel to the reciprocating slide guide means and intersectsthe reference axis at a right angle. A shaft, with a spindle headsecured to it, is supported in the pivot bearing means. Inside thespindle head, a spindle sleeve is guided so as to be displaced by meansof a feed drive along a grinding spindle axis which intersects the pivotaxis at a right angle. The spindle sleeve, which thus corresponds to afeed slide, includes a grinding spindle adapted to be driven in rotationand carrying a plate-shaped grinding disc for sharpening the toothing ofa circular saw blade. When straight surfaces at the front of teeth(cutting faces) or straight surfaces at the back of teeth (clearancefaces) are to be sharpened the spindle sleeve always is adjusted by thefeed drive in such a way that the active front surface of the grindingdisc will lie in a plane which contains the reference axis. For thegrinding of oblique surfaces, the spindle head is swung about the pivotaxis in one or the other direction, depending on the direction of theinclination. To accomplish that, a cross bar is fastened to that end ofthe shaft carrying the spindle head which is remote from the spindlehead, and two rolls are supported so as to be freely rotatable on thiscross bar at equal distances from the pivot axis and diametricallyopposed with respect to the latter. These two rolls are arranged betweena piston and cylinder unit each and an adjustable stop each in such away that the cross bar and, together with it, the shaft carrying boththe cross bar and the spindle head are swingable back and forth within apivot range which is limited by the stops. The inert masses thus to bemoved are considerable indeed because the spindle sleeve and its feeddrive take part in the pivoting motion. Consequently the pivotingfrequency to be achieved with back and forth swinging movements islimited.

SUMMARY OF THE PRESENT INVENTION

It is the object of the invention to improve a machine for machiningworkpieces which have cutting teeth, especially saw blades, such that itcan operate faster than the known machine described when machiningsurfaces at the front or back of teeth which are oblique in alternatingdirections or chamfers.

The object is met, in accordance with the invention, by the features ofclaim 1. Advantageous further developments are the subject matter of thesubclaims.

The principle which has been essential so far for the design ofmachinery for sharpening the serration of saws according to which theactive face of the tool had to be disposed such as to be touched by thepivot axis of the tool head, which pivot axis intersected the referenceaxis of the machine, is given up in accordance with the invention.According to the invention, neither the feed slide nor the reciprocatingslide take part in pivoting movements of the tool head about the pivotaxis. As a result, the inert mass affected by the swinging motions isonly relatively small and for this reason the pivoting can be effectedat high speed.

The pivot axis may be located at a distance in the order of up to aboutone tenth of the tool diameter from the active face of the tool,especially from the active front surface of a plate or cup-shaped tool.The influence of this distance on the machining geometry can becompensated by measures according to the invention in such a way that,once the cutting teeth are finished, it cannot be determined whetherthey were machined with the machine according to the invention or aknown machine. Machining, in the first place, is to be understood asreferring to the removal of material by grinding, but also by sparkerosion in cases suitable for such work. Accordingly, the tool to befastened on the tool spindle may be a grinding disc or an erosion disc.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will be described in greater detail belowwith reference to diagrammatic drawings, in which:

FIG. 1 is a front elevation of a machine for sharpening circular sawblades;

FIG. 2 is the view as seen in the direction of arrow II in FIG. 1;

FIG. 3 is the top plan view as seen in the direction of arrow III inFIG. 2;

FIG. 4 is the sectional elevation IV—IV in FIG. 2;

FIG. 5 shows an enlarged cutout of FIG. 4, and

FIG. 6 shows a modification of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The example shown of a workpiece 10 to be machined on the machineillustrated is a circular saw blade having hard metal trimmed cuttingteeth 12, each to be machined at its tooth face 14 and its tooth back 16while its tooth tip 18 is located in a predetermined position on astationary reference axis A of the machine.

The machine illustrated comprises a machine bed 20 and, on the same, astationary horizontal feed slide guide means 22 along which a feed slide24 is guided by means of a numerically controlled electric motor 26,especially a servo motor or a stepping motor, so as to be displaced by afeed spindle 28. The respective position of the feed slide 24 ismonitored by a distance measuring means 30.

A vertical reciprocating slide guide means 32 is disposed at the feedslide 24, and a reciprocating slide 34 is movable up and down along saidguide means by a numerically controlled electric motor 36, especially aservor motor or a stepping motor, via a lift spindle 38, while beingmonitored by a distance measuring means 40. The reciprocating slide 34has a built-in pivot bearing means 42 which defines a pivot axis B inparallel with the reciprocating slide guide means 32, i.e. a verticalpivot axis in the embodiment shown. The pivot axis B is the axis of apivot shaft 44 which is supported in the pivot bearing means 42 andcarries a tool head 46 fastened to its lower end.

A bearing box 50 is secured in the tool head 46 in electricallyinsulated manner through an insulation sleeve 48 and defines a spindleaxis C which is horizontal in the embodiment shown and intersects thepivot axis B at right angles. This is the axis of a tool spindle 52which is supported in the bearing box 50 and connected to a motor 56 bya belt drive means 54. The motor 56 is embodied by an electric motor fedby a frequency converter such that the tool spindle 52 can be driven atrotational speeds which are variable within wide limits.

The reciprocating slide 34 has an upper projecting arm 58 on which apivot drive means 60 is mounted to swing the tool head 46. The pivotdrive means 60 comprises a numerically controlled motor 62, especially aservo motor or stepping motor, and stepdown gearing 64 with a firsttoothed belt 66 which interconnects the shaft of the motor 62 and anintermediate gear 68 supported by the projecting arm 58, and furtherwith an intermediate pinion 70 which is firmly connected to theintermediate gear 68 and linked by a second toothed belt 72 to a gear 74fixed on the pivot shaft 44.

The pivot drive means 60 is adjusted, under program control, such thatthe tool head 46 will be in its normal position, illustrated in FIGS. 1to 5, at which the spindle axis C extends perpendicularly to thereference axis A, when a straight tooth face 14 or a straight tooth back16 are to be ground. The tool head 46 can be swung by the pivot drivemeans 60, under program control, into inclined positions towards eitherside from its normal position in order to sharpen cutting teeth 12 withan oblique tooth face 14 or an oblique tooth back 16 or in order tochamfer the edges between a tooth back 16 and lateral flanks of acutting tooth 12.

A workpiece slide guide means 76 is supported on the machine bed 20 forpivoting movements about the reference axis A and can be set at aposition which corresponds to the clearance angle or the cutting angleof the cutting teeth 12, depending on whether the latter are to bemachined at their tooth back 16 (FIG. 4) or their tooth face 14 (FIG.6). The workpiece slide guide means 76 guides a workpiece slide 78 whichis adjustable by an adjusting device 80, operated manually in theembodiment shown, and includes a workpiece support 82 for a workpiece10. Since the workpiece 10 is a circular saw blade in the embodimentillustrated the workpiece support 82 comprises a peg, as usual, on whichthe workpiece 10 is donned so as to be rotatable about its workpieceaxis of rotation D in order to be pushed forward in stepwise fashionsuch that after each step a machining position will be reached at whichthe tooth tip 18 of one of the cutting teeth 12 is located on thereference axis A.

An advance means 84 is provided to effect those forward movements. Thismeans is supported on the machine bed so as to be pivotable about abearing axis E parallel to the reference axis A, and it comprises anadvancing slide guide means 86 which is disposed at right angles to thereference axis A and along which an advancing slide 88 is guided forback and forth movement. The advancing slide 88 carries an advancefinger 90 for engagement with a respective tooth face 14 each in orderto push t e corresponding cutting tooth 12 into its position formachining. The advancing slide 88 carries a cam follower 92 by which itrests on a cam surface of an eccentric member 94 mounted on the machinebed 20 in pivotably adjustable fashion. Details of this arrangement areto be gathered from patent application 197 46 232 of Oct. 20, 1997.

A clamping device 96 of conventional design is provided to clamp theworkpiece 10 after each incremental movement.

The motor 26 and the distance measuring means 30 for the feed slide 24,the motor 36 and the distance measuring means 40 for the reciprocatingslide 34, and the motor 62 and an angle measuring means (not shown) forthe pivoting adjustments of the tool head 46 about the pivot axis B allare connected to a numerical control means 98.

The example shown of a tool 100 to be fastened on the tool spindle 52 ofthe machine illustrated either is a cup-shaped grinding disc forgrinding the cutting teeth 12 at their tooth back 16 (FIGS. 1, 4, and 5)or a plate-shaped grinding disc for grinding the cutting teeth 12 attheir tooth face 14 (FIG. 6). In both instances the tool 100 comprises abase 102 made of steel and a grinding layer 104 which is secured to thebase and the free front surface of which presents the active face 106 ofthe tool 100. The grinding layer 104 contains electrically conductivematerial. The tool 100 thus being electrically conductive on the whole,forms part of a measuring means 108 indicated in FIG. 6 including anelectric circuit which is closed through the tool 100 and the respectivecutting tooth 12 to be machined when the two contact each other.

The machining position of the cutting tooth 12 is known either as aresult of manual adjustment of the workpiece 10 by means of theadjusting device 80 or by program controlled sensing and adjusting inaccordance with DE 196 30 057 C1. Thus it may be assumed that the toothtip 18 of the cutting tooth 12 to be machined is located on thereference axis A. The numerical control means 98 then causes thereciprocating slide 34 to carry out several operating strokes in orderto determine the location of the active face 106 of the tool 100 as thatvaries in the course of wear. During those operating strokes, the activeface 106 of the tool 100 first is at a safe spacing from the tooth back16 (FIG. 4) or the tooth face 14 (FIG. 6) of the workpiece 10 and 6meanwhile the feed slide 24 is slowly advanced until the tool 100, byits active face 106, touches the tooth back 16 or the tooth face 14,whereby the electric circuit of the measuring means 108 is closed. Theposition of the feed slide 24 at which that happens is determined by thedistance measuring means 30. The position of the pivot axis B withrespect to any desired zero point of the distance measuring means 30 isknown from the beginning. The numerical control means 98, therefore, nowcan calculate the distance x between the pivot axis B and the activetool face 106 in its instantaneous state of wear.

If it is a straight tooth face 14, i.e. a tooth face in parallel withthe reference axis A, or a straight tooth back 16 which is to bemachined, no further calculating operations are required, apart from thefact that the tool 100 is moved forward by the feed slide 24 in theusual manner by an amount commensurate with that which is to be removedfrom the tooth face 14 or the tooth back 16.

However, when a tooth face 14 or a tooth back 16 is oblique, beinginclined at an angle α with respect to the workpiece axis D, it is notsufficient to swing the tool head 46 accordingly about the pivot axis B.What is needed in addition is an infeed z of the feed slide 24 adaptedto the distance x as measured and the angle of inclination α of the toolhead. This infeed z is calculated by the numerical control means 98 inaccordance with the geometrical relationships illustrated in FIG. 5,applying the following formula

z=y−x=x(1/cosα−1).

The infeed z is a negative amount when the distance x is positive, asillustrated in FIGS. 4 and 6.

The amount x gradually decreases as the wear of the tool 100 increases.But in the case of the tool 100 shown in FIG. 6 the distance x remainspositive until the grinding layer 104 is completely worn because thepivot axis B extends through the base 102. The situation is differentwith the tool 100 shown in FIGS. 4 and 5 where the pivot axis B extendsbetween the base 102 and the active face 106 when the grinding layer 104is new. Consequently the distance x becomes reduced with increasing wearof the grinding layer 104 according to FIG. 4 down to zero and, as thewear goes on, its value becomes negative and that requires positiveinfeed for machining oblique tooth backs 16.

Negative infeed is needed also when a cutting tooth 12, having had itstooth back 16 ground, is to be given a chamfer i.e. to receive a bevelgrind of limited width each at the transitions from its tooth back 16 toeither of its lateral flanks.

What is claimed is:
 1. A machine for machining workpieces (10) havingcutting teeth (12), especially saw blades, comprising a machine bed (20)which defines a reference axis (A), a workpiece support (82) on which aworkpiece (10) can be arranged such that the tooth tip (18) of a cuttingtooth (12) to be machined will lie on the reference axis (A), a toolhead (46) in which a tool spindle (52) adapted to be equipped with adisc-shaped tool (100) is supported so as to be driven in rotation abouta spindle axis (C), and an assembly for movably supporting the tool head(46) on the machine bed (20) which assembly comprises a reciprocatingslide (34) movable back and forth along a reciprocating slide guidemeans (32) transversely of the reference axis (A), a feed slide (24)adapted to be advanced along a feed slide guide means (22) transverselyof the reciprocating slide guide means (32), and a pivot bearing means(42) defining a pivot axis (B) parallel to the reciprocating slide guidemeans (32) about which axis the tool head (46) is pivotable by a pivotdrive means (60), with respect to the reciprocating slide (34) and theguide means (32) thereof, from a normal position at which surfaces ofthe cutting teeth (12) extending parallel to the reference axis (A) areto be machined by means of an active face (106) of the tool (100), intoinclined positions at which oblique surfaces of the cutting teeth (12)are to be machined by means of the same active face (106) of the tool(100), and further comprising a numerical control means (98) by which atleast the feed slide (24) is controllable, characterized in that, thetool head (46) is pivotable by the pivot bearing (42) also with respectto the feed slide (24) and the guide means (22) thereof, a measuringmeans (108) is provided to measure a distance (x) by which the activeface (106) of the tool (100) is spaced from the pivot axis (B), and thenumerical control means (98) is programmable such that it causes thefeed slide (24) to adopt a position at which the spacing of the pivotaxis (B) from the reference axis (A) equals the distance (x) when thetool head (46) is in the normal position, and it moves the feed slide(24) into a respective corrected position when the tool head (46) ispositioned at an inclination.
 2. The machine as claimed in claim 1,characterized in that the measuring means (108) comprises an electriccircuit which is closed through the tool (100) and the workpiece (10)when the two touch each other.
 3. The machine as claimed in claim 2,characterized in that the tool (100), being part of the measuring means(108), is adapted to be driven at a rotational measuring speed which isconsiderably slower than the rotational operating speed.
 4. The machineas claimed in claim 3, characterized in that the rotational measuringspeed lies in the order of magnitude between one and 10% of therotational operation speed.
 5. The machine as claimed in any one ofclaims 1 to 4, wherein the tool (100) is a cup-shaped grinding discwhich comprises a disc-shaped base (102) and a grinding layer (104) ofwhich the front end surface presents the active face (106) of the tool(100), and the pivot axis (B) extends between the active face (106) andthe base (102) when the grinding layer (104) is new.
 6. The machine asclaimed in any one of claims 1 to 4, wherein the tool (100) is aplate-shaped grinding disc which comprises a base (102) and a grindinglayer (104) of which the front end surface presents the active face(106) of the tool (100), and the pivot axis (B) extends between theactive face (106) and the base (102) when the grinding layer (104) isnew.